1. Field of the Invention
The present invention is directed to a vaporizer for vaporizing a liquid anesthetic of the type having a chamber containing liquid anesthetic, an inlet and an outlet with a gas flow passage, containing a throttle, therebetween, and a first connection between the chamber and the gas flow passage upstream of the throttle and a second connection between the chamber and the gas flow passage downstream of the throttle.
2. Description of the Prior Art
The manual "Halothane Vaporizer 950, Enflurane Vaporizer 951, Isoflurane Vaporizer 952 " describes a vaporizer of the above type. The vaporizer has a gas flow passage for a gas, a chamber for liquid anesthetic and an adjustable throttle. An opening is arranged between the gas flow passage and the chamber upstream from the adjustable throttle. Downstream from the adjustable throttle, a capillary tube is arranged with one nozzle end opening into the gas flow passage and the other end immersed in the liquid anesthetic in the chamber.
The presence of a gas flow causes pressure to drop across the adjustable throttle. The higher pressure upstream from the throttle is propagated through the opening into the chamber and exerts pressure on the surface of the liquid, forcing the liquid up into the capillary tube. The liquid is then sprayed out of the nozzle into the gas flowing in the gas flow passage and is vaporized.
The pressure drop across the throttle depends on the throttle's setting and controls the dispensing of the liquid. Changing the throttle setting makes it possible to achieve different concentrations of anesthetic in the gas.
The known ventilator has an accuracy of .+-.10% of the value which is set, which is an accuracy that is sufficient for all applications in conjunction with anaesthesia. This known vaporizer, however, has certain disadvantages.
One disadvantage is that each time a flow of gas is supplied to the vaporizer to dispense anesthetic, working pressure in the vaporizer needs to build up first. This causes a slight but nevertheless measurable delay in dispensing. Moreover, the chamber must fill with gas before any pressure can be exerted on the surface of the liquid. A small loss in gas volume occurs on occasions when the chamber only holds a small amount of liquid. This loss has an effect on the concentration of dispensed anesthetic.
Even if these disadvantages only have a minor, virtually insignificant, impact on vaporizer operation, additional functional refinement would still be desirable.
Another disadvantage of this known vaporizer is that it is not suitable for use with all ordinary anesthetic agents. As a result of its low boiling point, the anesthetic desflurane is particularly unsuitable for use in this known vaporizer.